1. Field of the Invention
Embodiments of the invention relate to seismic exploration in marine environments.
2. Description of the Related Art
Seismic exploration operations generally utilize a seismic energy source to generate an acoustic signal that propagates into the earth. The acoustic signal is partially reflected by subsurface seismic reflectors in the earth, which may include interfaces between subsurface lithologic or fluid layers that may be characterized by different elastic properties. The reflected signals are detected and recorded by seismic receiver units located at or near the surface of the earth, thereby generating a seismic survey of the subsurface. The recorded signals, or seismic energy data, can then be processed to yield information relating to the lithologic subsurface formations, identifying such features, as, for example, lithologic subsurface formation boundaries.
Generally, the method for detection and recording of seismic signals is similar on land and in marine environments; however, marine environments present unique challenges due to the body of water overlaying the earth's surface. Seismic exploration operations in marine environments are typically conducted from the deck of one or more seismic exploration vessels, such as floating platforms or ships. The seismic exploration vessels typically provide storage and transportation for a plurality of seismic receiver units and associated operational equipment. Seismic exploration in deep water typically uses seismic sensor units deployed from the deck of the seismic exploration vessel to be placed on or near the seabed. These seismic sensor units are part of systems typically referred to as Ocean Bottom Cabling (OBC) or Ocean Bottom Seismometer (OBS) systems, wherein data from a seismic survey may be received.
In order to realize a safe and efficient seismic operation on the deck of the vessel, which typically has limited open space, organization of both equipment and personnel is required in order to maintain safety and efficiency. Thus, even in fair weather and calm sea conditions, simple deployment and retrieval of seismic receiver units in marine environments must be conducted methodically with due care. Further, as the vessel may be operated in harsh weather conditions, such as high seas and wind, the safety and efficiency of the seismic operation is more difficult to maintain. These factors have become even more significant as exploration operations have moved to deeper and deeper water, where operations require longer periods of offshore time.
Conventionally, sensor units are stored on the deck of the vessel in crate-like devices or static storage racks that require individual sensor units to be handled multiple times by personnel on the vessel. In some conventional systems, a robotic device may be used to remove individual sensor units from storage racks; however, robotic devices require a large amount of deck space to operate, thereby limiting the deck space available for sensor storage, retrieval and deployment.
Thus, there is a need for an improved method and apparatus for deployment and retrieval of sensor units from the deck of a seismic exploration vessel.